Former British prime minister Tony Blair has acknowledged that he ignored the warning of his then-Attorney General that attacking Iraq was illegal without United Nations approval.
Mr Blair, who was summoned on Friday for a second time by the official inquiry into Britain's role in the Iraq war, said he believed the warning was provisional.
During a four hour appearance, he said he thought the Attorney General would change his mind on whether a second UN resolution was necessary when he knew the full details of negotiations that had been taking place.
Mr Blair said he regrets deeply and profoundly the loss of life during and after the 2003 Iraq war.
The ex-PM said his refusal to express regret for the decisions that led to war at his first appearance before the committee had been misinterpreted.
But his words were met with cries of too late from the public gallery. The BBC reports Committee chairman Sir John Chilcot had to tell the public gallery to be quiet.
Looming challenge from Iran
Mr Blair also urged the West to stop apologising for its actions in Iraq and warned of the threat from Iran.
Asked whether what had happened in Iraq had made the risk from Iran and other countries developing nuclear weapons worse, rather than better, he said: I don't think so.
Mr Blair, who is now a UN Middle East peace envoy, said there was a looming and coming challenge from Iran.
I am out in that region the whole time. I see the impact and influence of Iran everywhere, he said. It is negative, destabilising and it is supportive of terrorist groups.
It is doing everything it can to impede progress in the Middle East peace process, and to facilitate a situation in which that region cannot embark on a process of modernisation it so urgently needs.
And this is not because we have done something, said Mr Blair.
At some point - and I say this to you with all the passion I possibly can - the West has got to get out of what I think is this wretched policy, or posture, of apology for believing that we are causing what the Iranians are doing, or what these extremists are doing. The fact is we are not.
The fact is they are doing it because they disagree fundamentally with our way of life and they will carry on doing it unless they are met with the requisite determination and, if necessary, force.
Britain joined the invasion of Iraq in March 2003 despite failing to secure a second UN resolution justifying the use of force.
The Chilcot inquiry was announced in June 2009 after the last British troops left Iraq. The hearings began in November 2009,
Mr Blair previously appeared in January 2010 when he was questioned for six hours.
He said the war made the world a safer place and he has no regrets about removing Saddam Hussein.
The committee is expected to publish its report later this year.